Diene rubbers such as natural rubbers, isoprene rubber, SBR and BR have been widely used for tires, automotive parts, industrial parts, etc. because of their excellent processability and strength. Further, natural rubbers are excellent in dynamic fatigue resistance.
However, the diene rubbers have a problem of short life on account that they are low in weathering resistance and ozone resistance, and especially natural rubbers are low in heat resistance and ozone resistance.
As rubber materials for automotive tire tread, diene rubbers such as blends of styrene/butadiene copolymer rubbers and a polybutadiene rubber have been generally used. However, the tire tread formed from only the styrene/butadiene copolymer rubber has high rolling resistance and low abrasion resistance because of its low repulsion elasticity at 50.degree. to 70.degree. C., though it is relatively good in damping properties on the wet road surface (wet skid). For coping with this problem, there has been used a blend obtained by blending 100 parts by weight of the styrene/butadiene copolymer rubber with 10 to 50 parts by weight of the polybutadiene rubber.
With the request of saving energy in recent years, drastic reduction of the fuel cost and high abrasion resistance have been demanded, and in addition, damping properties on the wet road surface has been also demanded from the viewpoint of safety. However, the blend of the conventional styrene/butadiene copolymer rubber and the polybutadiene rubber is insufficient in the damping properties.
For improving those properties, a blend of a halogenated butyl rubber and a polybutadiene rubber has been proposed, but this blend is still insufficient in the damping properties, the abrasion resistance and the rolling resistance.
Hence, the advent of a rubber composition for tire tread which is particularly excellent in the abrasion resistance and the damping properties on the wet road surface and can be prominently reduced in the rolling resistance is also desired.
In constrast with the above diene rubbers, ethylene/propylene/diene (EPDM) copolymers have been widely used for rubber products such as automotive industrial parts, industrial rubber products, electrical insulating materials, civil engineering and building materials and rubberized fabrics; and plastic blend materials for polypropylene and polystyrene because of their high heat resistance and ozone resistance.
However, the EPDM copolymers are not applied to some special uses, for example, rubber vibration insulator, rubber roll, belt, tire, cover materials for vibrating portions, etc. because of their poor dynamic fatigue resistance.
With respect to copolymers of higher .alpha.-olefins and non-conjugated dienes, U.S. Pat. Nos. 3,933,769, 4,064,335 and 4,340,705 disclose a copolymer of a higher .alpha.-olefin, methyl-1,4-hexadiene and an .alpha.,.omega.-diene. The methyl-1,4-hexadiene is a mixture of 4-methyl-1,4-hexadiene and 5-methyl-1,4-hexadiene, and these monomers differ in the reaction rate from each other. Accordingly, when continuous polymerization is conducted, it is difficult to recover those monomers for the repeated use. Further, 4-methyl-1,4-hexadiene is different from 5-methyl-1,4-hexadiene in the copolymerization reactivity with the higher .alpha.-olefin, and hence there is involved such a problem that the monomer conversion is low and the polymerization efficiency is bad. Moreover, use of the .alpha.,.omega.-diene sometimes causes occurrence of gel in the resulting copolymer thereby to give an adverse effect to physical properties of the final product.
In the processes for preparing higher .alpha.-olefin copolymers described in the above specifications, titanium trichloride catalysts or catalysts formed from titanium tetrachloride and organoaluminum are used, and therefore the catalytic activity is not sufficiently high, resulting in a disadvantage of high production cost.
Accordingly, eagerly desired is the advent of a copolymer which is available at a low cost and is excellent in not only dynamic fatigue resistance (flexural fatigue resistance), weathering resistance, ozone resistance, thermal aging resistance and low-temperature characteristics but also processability, compatibility with aromatic ring-containing polymers such as SBR and covulcanizability therewith.
U.S. Pat. No. 4,645,793 discloses a blend of a diene rubber and an ethylene/.alpha.-olefin copolymer, which is improved in the weathering resistance and the ozone resistance Though this blend of the diene rubber and the ethylene/.alpha.-olefin copolymer is improved in the weathering resistance and the ozone resistance, it tends to be reduced in dynamic fatigue resistance (flexural fatigue resistance) or lowered in adhesion to fibers.
Accordingly, a vulcanizable rubber composition excellent in not only processability, strength, weathering resistance, ozone resistance and dynamic fatigue resistance but also adhesion to fibers has been conventionally desired.
Accordingly, there is desired the advent of long-life rubber molded products which are excellent in both of environmental aging resistance such as thermal aging resistance, weathering resistance, ozone resistance, etc., abrasion resistance, damping properties on the wet road surface, processability, compatibility with aromatic ring-containing polymers such as SBR, covulcanizability therewith, adhesion to fibers and dynamic fatigue resistance (flexural fatigue resistance).
The present inventors have earnestly studied on such copolymer, vulcanizable rubber composition, particularly rubber composition for tire tread, and molded products as mentioned above. As a result, they have found the followings and accomplished the present invention.
(1) When a specific higher .alpha.-olefin, a specific non-conjugated diene and a specific aromatic ring-containing vinyl monomer are copolymerized with each other in the presence of a specific catalyst for an olefin polymerization, there can be obtained a higher .alpha.-olefin copolymer which is excellent in not only dynamic fatigue resistance (flexural fatigue resistance), weathering resistance, ozone resistance, thermal aging resistance and low-temperature characteristics but also in processability, compatibility with aromatic ring-containing polymers such as SBR and covulcanizability therewith. PA1 (2) When a copolymer obtained by copolymerizing a specific higher .alpha.-olefin, a specific non-conjugated diene and a specific aromatic ring-containing vinyl monomer in the presence of a specific catalyst for an olefin polymerization is blended with a diene rubber, there can be obtained a higher .alpha.-olefin copolymer rubber composition which is excellent in not only processability, strength, weathering resistance, ozone resistance and dynamic fatigue resistance but also adhesion to fibers. PA1 (3) When a higher .alpha.-olefin copolymer obtained by copolymerizing a specific higher .alpha.-olefin, a specific aromatic ring-containing vinyl monomer and a specific non-conjugated diene in the presence of a specific catalyst for an olefin polymerization is blended with a diene rubber, there can be obtained a rubber composition for tire tread which is particularly excellent in both of abrasion resistance and damping properties on the wet road surface and can be prominently reduced in the rolling resistance. PA1 (4) When a higher .alpha.-olefin copolymer obtained by copolymerizing a specific higher .alpha.-olefin, a specific non-conjugated diene and a specific aromatic ring-containing vinyl monomer in the presence of a specific catalyst for an olefin polymerization is vulcanized, there can be obtained a higher .alpha.-olefin copolymer rubber molded product which has a long life and is excellent in not only environmental aging resistance but also dynamic fatigue resistance (flexural fatigue resistance). PA1 (i) a molar ratio of the higher .alpha.-olefin to the aromatic ring-containing vinyl monomer ranging from 95/5 to 30/70, PA1 (ii) a content of the non-conjugated diene ranging from 0.01 to 30% by mol, and PA1 (iii) an intrinsic viscosity [.eta.], as measured in decalin at 135.degree. C., of 0.1 to 10 dl/g; ##STR3## wherein n is an integer of 0 to 5, R.sup.1, and R.sup.2 and R.sup.3 are each independently a hydrogen atom or an alkyl group of 1 to 8 carbon atoms; ##STR4## wherein n is an integer of 1 to 5, R.sup.4 is an alkyl group of 1 to 4 carbon atoms, and R.sup.5 and R.sup.6 are each independently a hydrogen atom or an alkyl group of 1 to 8 carbon atoms, provided that both of R.sup.5 and R.sup.6 are not hydrogen atoms. PA1 (a) a solid titanium catalyst component containing magnesium, titanium, halogen and an electron donor as its essential components, PA1 (b) an organoaluminum compound catalyst component, and PA1 (c) an electron donor catalyst component; PA1 [A] a higher .alpha.-olefin copolymer of a higher .alpha.-olefin having 6 to 20 carbon atoms, an aromatic ring-containing vinyl monomer represented by the above formula [I] and a non-conjugated diene represented by the above formula [II], and PA1 [B] a diene rubber, PA1 [A] a higher .alpha.-olefin copolymer of a higher .alpha.-olefin having 6 to 20 carbon atoms, an aromatic ring-containing vinyl monomer represented by the above formula [I] and a non-conjugated diene represented by the above formula [II], and PA1 [B] a diene rubber, PA1 (i) a molar ratio of the higher .alpha.-olefin to the aromatic ring-containing vinyl monomer [higher .alpha.-olefin/aromatic ring-containing vinyl monomer] ranging from 95/5 to 30/70, PA1 (ii) a content of the non-conjugated diene ranging from 0.1 to 20% by mol, and PA1 (iii) an intrinsic viscosity [.eta.], as measured in decalin at 135.degree. C. of 0.1 to 10 dl/g